Raman spectroscopy is a spectroscopic technique widely used to identify molecules and study rotational and vibrational modes in molecular systems. To perform Raman spectroscopy, a monochromatic beam of light with a fixed wavelength is directed at a sample, and a spectrum of scattered light reflected from the sample is collected as a Raman spectrum. The collected Raman spectrum is then used to characterize the sample, for example, by identifying or detecting one or more molecules therein. Although generally an effective way to characterize a sample, traditional Raman spectroscopy techniques suffer from a relatively low sensitivity. In other words, traditional Raman spectroscopy techniques may be unsuitable for identifying or detecting relatively small concentrations of molecules in a given sample.
One way to improve the sensitivity of traditional Raman spectroscopy techniques is through the use of surface-enhanced Raman spectroscopy (SERS). To perform SERS, a sample is placed on a nano-patterned metal surface, and a monochromatic beam of light with a fixed wavelength is directed incident to the nano-patterned metal surface. The intensity of the spectrum of scattered light reflected from the sample on or near the nano-patterned metal surface can be much higher than that obtained using a traditional Raman spectroscopy technique. Accordingly, SERS is a powerful tool that allows for the detection of molecules in highly diluted solutions, and in some cases, may even enable the detection of a single molecule in a solution. Although highly effective for increasing the sensitivity of traditional Raman spectroscopy techniques, SERS is generally unsuitable for in-vivo detection of target molecules in various environments, as it requires a sample to be placed on the nano-patterned metal surface, which in turn must be arranged in proximity to a light emitting device such that a beam of light can be directed incident to the nano-patterned metal surface. In other words, current SERS techniques require multiple components that must be arranged in a specific fashion (generally requiring a relatively large amount of space) to generate a reliable result, thereby precluding the use of SERS within a given environment. Additionally, the nano-patterned metal surface used in current SERS techniques often suffers from oxidation and/or other degradation problems over time, resulting in a decrease in the intensity of scattered light reflected from the surface. Due to oxidation and/or other degradation, the nano-patterned metal surface is generally only used once, then discarded, resulting in an increase in the operating cost of a SERS system. Finally, the nano-patterned metal surface used in current SERS techniques is generally difficult to manufacture on a large scale, often resulting in high cost, low reproducibility, or both.
Accordingly, there is a need for an improved surface for use with SERS techniques that is highly sensitive, resistive to oxidation and other degradation, and capable of manufacture on a large scale at a reasonable cost. Further, there is a need for a SERS system capable of use for in-vivo and in-vitro applications.